Macrowine 2021
IVES 9 IVES Conference Series 9 Evolution of flavonols during Merlot winemaking processes

Evolution of flavonols during Merlot winemaking processes

Abstract

Aim: The phenomenon of quercetin precipitation in wine (flanovol haze), has been manifested for many years in several wine-producing regions, such as Italy, Australia, and New Zealand (Gambuti et al., 2020; Lanati, Marchi, & Cascio, 2014; Somers & Ziemelis, 1985). Due to the limited information related to the quercetin aglycone behavior and its precursors during wine production in New Zealand, this study aims to monitor the evolution of flavonols and other polyphenols during the commercial fermentation of Merlot grapes, using different fermentation conditions, and vineyard treatments.

Methods: Various trials evaluating sun exposure, winemaking practices, and winemaking process management were undertaken using Merlot grapes, commercial yeast cultures, potassium metabisulphite (20 g/hL), and nutrient supplementation with DYNASTART®-LAFFORT at 20 g/hL. Samples were taken through the winemaking stages, and the polyphenols were quantified using a reversed-phase HPLC method (Garrido-Bañuelos et al., 2019; Peng et al. 2002).

Results: Grapes with elevated amounts of flavonols glycosides produced wines with higher levels of flavonol glycosides and quercetin. Wines made from grapes with greater sun exposure ended up with more flavonol glycosides (89 mg/L) and quercetin (16 mg/L) than the wines elaborated from less exposed grapes (47 mg/L and 9.4 mg/L, respectively). Certain winemaking practices showed differences in quercetin content, for example using small fermentation (250 kg) (12 mg/L), and large fermentation (five tonnes) (28 mg/L). The data also indicates that tannins and total anthocyanins were present at 786 mg/L and 156 mg/L, respectively, for small-scale ferments, and at 888 mg/L and 363 mg/L, respectively, for large-scale ferments. In evaluating the winemaking process management, the ferment pumped over (largest fermentation volume) exhibited flavonol glycosides and quercetin at the highest concentration (91 mg/L and 20 mg/L, respectively), compared to the remaining treatments. PMS, enzyme, and PMS plus enzyme, additions lowered the concentration of the flavonols glycosides at the end of the winemaking process (37 mg/L, 42 mg/L, and 43 mg/L, respectively). It was seem that the PMS plus enzyme (15.6 mg/L) increase quecetin in wine when compared to the control, no additions, (12.6 mg/L). The wines treated with enzyme, PMS, and PMS plus enzyme, also had lower concentrations of anthocyanins (215 mg/L, 233 mg/L, and 238 mg/L, respectively) than the control (291 mg/L). 

Conclusions

The study confirmed past research on the role of sun exposure in the formation of flavonols in Merlot grapes and wines. Fermentation size can improve the extraction of polyphenols into wine, and the enzyme additions can promote the hydrolysis of flavonol glycosides. In considering winemaking practices to lower flavonol content, the impact on remaining wine phenolics, of importance to wine colour and mouthfeel, also needs to be carefully evaluated.

DOI:

Publication date: September 14, 2021

Issue: Macrowine 2021

Type: Article

Authors

Cristian Hernandez

School of Chemistry University of Auckland,Paul KILMARTIN, School of Chemistry, University of Auckland Leandro DIAS, School of Food Science, University of Auckland Gianni FLEGO, Villa Maria Estate winery Rebecca DEED, School of Biological Sciences, University of Auckland

Contact the author

Citation

Related articles…

Effect of vineyard management strategy on the nutritional status of irrigated « Tempranillo » vineyards grown in semi-arid areas

The combination of cover crops with regulated deficit irrigation has been lately shown to be a good method to improve harvest quality in irrigated vineyards of Southern Europe with semiarid climate, as an alternative to the conventional management, that consists on mechanical tillage and irrigation from fruitset to veraison and from then on reduced, or even ended.

Wine microbial diversity and cross-over applications: emerging results and future perspectives

AIM: Cross-over applications are an emerging technological approach in food microbiology where a microorganism from one traditional specific fermentation process is used to improve quality and safety in another agri-food production/chain (Dank et al., 2021). A complex microbial diversity is found in association with fermentation in wine, including Saccharomyces, non-Saccharomyces and malolactic bacteria,  all microorganisms versatile in terms of enological utilisation (Tempère et al., 2018). Here, we propose a systematic literature review highlighting the existing trends and possible future applications related to cross-over exploitation of wine-related microbiota. 

Molecularly imprinted polymers: an innovative strategy for harvesting polyphenoles from grape seed extracts

Multiple sclerosis (MS) is a multifactorial autoimmune disease associating demyelination and axonal degeneration developing in young adults and affecting 2–3 million people worldwide. Plant polyphenols endowed with many therapeutic benefits associated with anti-inflammatory and antioxidant properties represent highly interesting new potential therapeutic strategies. We recently showed the safety and high efficiency of grape seed extract (GSE), a complex mixture of polyphenolics compounds comprising notably flavonoids and proanthocyanidins, in an experimental autoimmune encephalomyelitis (EAE) mouse model of MS.

Geospatial trends of bioclimatic indexes in the topographically complex region of Barolo DOCG

Barolo DOCG is an economically important wine producing region in Northwest Italy. It is a small region of approximately 70 km2 gross area. The topography is very complex with steep sloped hills ranging in elevation from below 200 m to 550 m. Barolo DOCG wine is made exclusively from the Nebbiolo grape. Bioclimatic indexes are often used in viticulture to gain a better understanding of broader climate trends which can be compared temporally and geographically. These indexes are also used for identifying potential phenological timing, growing region suitability, and potential risks associated with expected climatic changes. Understanding how topography influences bioclimatic indexes can help with understanding of mesoscale climate behaviour leading to improved decision making and risk management strategies. The average monthly maximum and minimum temperatures, the Cool Night Index, the Huglin Index, and the monthly diurnal range (from July to October) were calculated using data from 45 weather stations within a 40 km radius of the Barolo DOCG growing area between the years 1996 and 2019. Linear and multiple regression models were developed using independent variables (elevation, aspect, slope) extracted from a digital elevation model to identify significant relationships. Bioclimatic indexes were then kriged with external drift using independent variables that showed significant relationships with the bioclimatic index using a 100 m resolution grid. The maximum monthly temperatures and the Huglin Index showed consistent significant negative relationships with elevation in all years. The minimum monthly temperatures showed no relationship with elevation but in some months a small but significant relationship was observed with aspect. Due to the lack of a relationship between minimum monthly temperatures and elevation compared to the significant relationship between maximum monthly temperatures and elevation, monthly diurnal range had a negative relationship with elevation.

Hyperspectral imaging and Raman spectroscopy, nondestructive methods to assess wine grape composition

Grape composition is of high interest for producing quality wines. For that, grape analyses are necessary, and they still require sample preparation, whether with classical analyses or with NIR analyses.